Pin diskimage-builder version due to drop Python3.6

Since Ibdbcf459608711ac64e7fefb1707f6708d68e750 merged to master we
need to pin diskimage-builder to latest stable tag with support of
the Python3.6 until we move to CentOS9.

Change-Id: I9f9e381716611b71584ecf8b371f8b7f45c694ee
Signed-off-by: Maksim Malchuk <[email protected]>
(cherry picked from commit 1b259ec)

Author: mmalchuk

docker/bifrost/bifrost-base/Dockerfile.j2

@@ -42,6 +42,11 @@ RUN echo " " && \
 {%- endif %}
     bash -c 'TOX_CONSTRAINTS_FILE=/requirements/upper-constraints.txt ./scripts/env-setup.sh && \
     ansible-playbook -vvvv -i /bifrost/playbooks/inventory/target /bifrost/playbooks/install.yaml \
+{%- if base_distro == 'centos' %}
+{# NOTE(mmalchuk): since DIB drop Python3.6 support we need to build DIB from #}
+{# the latest supported stable tag until we move to CentOS9 #}
+    -e dib_git_branch="3.21.1" \
+{%- endif %}
     -e @/tmp/build_arg.yml && \
 {%- if base_package_type == 'deb' %}
     apt-get clean && rm -rf /var/lib/apt/lists/*'